import numpy as np

arr2D = np.array([
    [1,2, 3, 4, 5],
    [6, 7, 8, 9, 10],
    [11, 12, 13, 14, 15]
])

index6 = np.where(arr2D == 6)
print(index6)

indexes_even = np.where(arr2D % 2 == 0)
print(indexes_even)